Automatic transmission control system having two accumulators for four clutches controlled by a single accumulator back pressure valve

Abstract

An automatic transmission control system includes a hydraulic circuit for controlling coupling pressure supplied to frictional coupling elements of the automatic transmission, which are selectively coupled and uncoupled so as to shift the automatic transmission into desired gears. The hydraulic circuit has a solenoid valve, for regulating a principal hydraulic pressure to provide a control pressure in accordance with vehicle driving conditions. The coupling pressure, supplied to a frictional coupling element, is regulated by a regulating valve in accordance with a control pressure level, and during shifting of the automatic transmission, is supplied through an accumulator whose back pressure is controlled in accordance with the control pressure by a control valve.

What is claimed is: 
     
       1. A control system for controlling an automatic transmission of a vehicle, which includes a hydraulic control circuit for controlling coupling pressure supplied to a plurality of frictional coupling elements of the automatic transmission which are (1) selectively coupled and uncoupled so as to shift the automatic transmission into desired gears and (2) divided into a first group of frictional coupling elements having a coupling pressure controlled in accordance with a control pressure and a second group of frictional coupling elements having a coupling pressure independent from said control pressure, said hydraulic control circuit comprising: driving condition detecting means for detecting driving conditions of the vehicle;   an oil pump for generating a hydraulic pressure;   solenoid valve means for regulating said hydraulic pressure so as to provide said control pressure in accordance with vehicle driving conditions detected by said driving condition detecting means;   regulating valve means, provided for each frictional coupling element in said first group, for regulating a coupling pressure supplied to each frictional coupling element in said first group in accordance with said control pressure;   accumulating means for controlling a supply of said coupling pressure of specified frictional coupling elements of said second group of frictional coupling elements during shifting of said automatic transmission; and   control valve means for controlling a back pressure supplied to said accumulating means in accordance with said control pressure.   
     
     
       2. A control system as defined in claim 1, wherein said accumulating means comprises at least two accumulators. 
     
     
       3. A control system as defined in claim 2, wherein said solenoid valve means is coupled to more than two regulating valves of said regulating valve means and at least two accumulators of said accumulating means. 
     
     
       4. A control system as defined in claim 1, and further comprising another valve means for regulating said hydraulic pressure supplied to said frictional coupling elements of said second group. 
     
     
       5. A control system for an automatic transmission of a vehicle, which includes a hydraulic control circuit for controlling coupling pressure supplied to a plurality of frictional coupling elements of the automatic transmission which are selectively coupled and uncoupled so as to shift the automatic transmission into desired gears, said hydraulic control circuit comprising: driving condition detecting means for detecting driving conditions of the vehicle;   an oil pump for generating a hydraulic pressure;   solenoid valve means for regulating said hydraulic pressure so as to provide a control pressure in accordance with vehicle driving conditions detected by said driving condition detecting means;   regulating valve means, provided for each of said frictional coupling elements, for regulating a coupling pressure supplied to each of said frictional coupling elements in accordance with said control pressure;   accumulating means for controlling a supply of said coupling pressure to said frictional coupling elements during shifting of said automatic transmission;   control valve means for controlling a back pressure supplied to said accumulating means in accordance with said control pressure; and   interrupting means for interrupting pressure regulation of said regulating valve means for at least one of said frictional coupling elements operatively connected to an accumulator of said accumulating means having a back pressure which is controlled by said control valve means.   
     
     
       6. A control system as defined in claim 5, and further comprising another solenoid valve means for regulating said hydraulic pressure supplied as a control pressure to said interrupting means.